Trivalent iodine compounds in which the iodine atom is attached to two aromatic rings to form an iodonium cation have been known for a number of years. (See for example Masson and Race, J. Chem. Soc. 1937 1716, and U.S. Pat. No. 2,878,293.) Beginning in 1947, Sandin and co-workers reinvestigated the preparation of dibenziodolium iodides which differ from the iodonium compounds of Masson in that the two phenyl rings are directly bonded. The original preparation of a dibenziodolium compound was published in 1908 by Mascarelli and Benati, Gazz. chim. ital. 38 624 (1908), but this work was apparently overlooked by Masson and Race. The Sandin work is contained in the following papers: Wasylewsky, Brown and Sandin, J. Am. Chem. Soc. 72, 1039 (1950) and Collette et al., J. Am. Chem. Soc. 78, 3819 (1956). The use of dibenziodolium compounds as bactericides is disclosed in U.S. Pat. No. 3,207,660 as well as in Australian Pat. No. 21749/62 and South African Pat. No. 63/4106 1964 (Derwent Farm. Doc. nos. 11012 and 12453). Certain extremely powerful microbiocidal halogen-substituted dibenziodolium salts are disclosed in U.S. Pat. No. 3,264,355. An excellent review of the chemistry of heterocyclic iodine compounds is contained in a review by Banks "Organic Polyvalent Iodine Compounds," Chemical Review 16, 243 (1966).
Heterocyclic iodine compounds in which the two phenyl rings are joined other than by a direct bond or by an alkyl group have not heretofore been known with one exception, an oxygen-bridged compound, 3,7-dinitrodibenz[be][1,4]oxiodinium iodide, was prepared by Hwang et al., K'o Hsueh T'ung Pao No. 2, 49-50 (1957), abstracted in Chemical Abstracts 53, 4280 (1959). Hwang et al. also stated that they were unable to prepare the corresponding thiaiodinium compound.